1. Field of the Invention
The invention relates to a facet mirror having a number of mirror facets that can be used in illuminating devices for projection exposure machines in microlithography, in particular when employing radiation in the region of the extreme ultraviolet.
2. Description of the Related Art
Tilting mirrors as mirror facets for facet mirrors comprising a number of these mirror facets are known from the prior art.
Thus, for example, GB 2 255 195 A describes such facet mirrors having individual tilting mirrors and appropriate bearing elements for the facet mirrors, whose intended use is to be looked for, in particular, in the field of solar energy technology.
Each individual one of the tilting mirrors is constructed in this case such that it comprises a mirror surface which is connected via a rod to a sphere which is fastened in appropriate bearing devices. The accuracy of such arrangements with regard to the possibility of adjusting them or the like is extremely limited in this case, since the individual tilting mirrors are held in a comparatively loose fashion and maladjustment can come about very easily and quickly.
In the case of such a design, it is therefore certainly impossible to implement the accuracies which are required in the adjustment and which are necessary for the case of application for the abovenamed invention in a projection exposure machine for microlithography, in particular for use with radiation in the region of the extreme ultraviolet (EUV). Furthermore, it is possible during adjustment to access the individual mirror facets only from the side of their reflecting surface, and so it is comparatively complicated and difficult to align the individual mirrors when they are illuminated.
Moreover, EP 0 726 479 A2 describes a tilting mirror arrangement which has at least one tilting mirror, a basic body and at least one mirror bearing with an at least virtually fixed fulcrum between the tilting mirror and the base. In accordance with the document, in the case of mirror surfaces with a characteristic length of less than 40 mm, the overall size of the total arrangement of tilting mirror bearing and tilting mirror housing is arranged below the reflecting surface in such a way that, when projected onto the mirror plane, it does not project beyond it, or does so only slightly when the tilting mirror is deflected. Such tilting mirrors are used, for example, in the field of laser technology.
Such mirrors can also be adjusted when illuminated, owing to the possibility of mounting the basic body correspondingly via the mirror bearing and readjusting it, if appropriate. However, the design is very complicated, and so a very high outlay on the overall space in the axial direction, the adjusting elements, the costs and the like is to be expected in the case of facet mirrors which could be formed from these tilting mirrors.
DE 23 63 765 discloses a bearing for a pivotable mirror for coherent optical systems. The mirror is arranged in this case on the circular surface of a spherical segment, the center of the sphere lying on the reflecting surface. The spherical segment is mounted in a spherical pan or spherical cap of corresponding diameter. The spherical segment is provided for the purposes of movement and control with a lever-shaped extension arranged radially relative to the sphere. In this case, the extension can be moved by means of an adjusting device active in a plane parallel to the plane of the neutral position of the mirror.
Reference may be made to U.S. Pat. No. 6,276,066 for the further prior art.